This is not entirely true, external becs are still used and nescesary depending on what you are trying to do.

Most ESC's with a BEC are designed to work comfortably with 3 servos, 4 is usually pushing it unless they're low torque servos, which isn't what you want to be using with a helicopter. This depends of course on the type of helicopter, small micros are usually okay since micro servos don't suck up too much amperage to begin with, but when you start going into larger models that require slightly more power such as the T-rex, eco 8, logo 10, etc. Most ESC's will choke out and burn up on 4 servos unless they're designed specfically for that purpose (as some ESC's are), at which point, an external BEC is needed, or a seperate receiver pack. Obviously an external BEC is preferred as it's lighter. If given the option I would go with an external bec, it simply puts less strain on the ESC, and keeps it running cooler.

Allthough, for the #36, you're probably OK using an ESC with a BEC in it.

Just though i'd point that out External BEC's are still needed for us fellas who fly the bigger helis